1. Field of the Invention
This invention relates to a slit exposure device, and more particularly, to a slit exposure device of the type with a fixed original carrier and a movable optical system. More specifically, the invention relates to a slit exposure device comprising improved optical system drive means of the type in which two or a group of moving mirrors are moved at a speed ratio of 2 : 1, and means for connecting a power source for illuminating an original.
2. Description of the Prior Art
Slit exposure devices of the type with a fixed original carrier and a movable optical system are known, and particularly, various optical systems of the type in which two moving mirrors or lenses are moved at a speed ratio of 2 : 1 are known, such as disclosed in U.S. Pat. Nos. 3,330,181; 3,431,053; 3,497,298; 3,062,108 and 3,689,145.
A conventional optical system drive device is illustrated in FIG. 1, which shows an original 2 to be copied, placed on a fixed original carrier 1 wherein an image of the original is formed on a photosensitive medium P, which passes through a slit 7, by an optical system consisting of mirrors 3 and 4, a fixed lens 8, and fixed mirrors 5 and 6. As the photosensitive medium moves forward in the direction as indicated by the arrow, the mirror 3 will move, in the direction as indicated by the arrow, at a predetermined speed relative to the moving speed of the photosensitive medium, while the mirror 4 will move, in the direction as indicated by the arrow, at a speed of 1/2 of the speed of mirror 3, whereby the slit exposure is effected, always maintaining a constant length of an optical path from the original 2 to the lens 8. When the mirrors 3 and 4 reach end positions 3' and 4' (as indicated by the dotted lines) from the exposure starting positions (as indicated by the full lines), they again move back to the exposure starting positions for accomplishment of the next exposure.
In this case, the optical system performs a reciprocating motion, and to obtain a better copied image, the above-described mirrors 3 and 4 must be moved by the strict maintenance of speed ratio on the order of 2 : 1. The simplest method for this purpose is to utilize the principles of the pulleys as shown in FIG. 1. As seen in FIG. 1, a wire 9 having one end thereof secured to a copying machine body is passed over a pulley 11 mounted on a bed 10 on which the mirror 4 is placed. The mirror 3 is placed on a bed 12, and when the other end of the wire is pulled by a suitable drive means, to the right as viewed in the figure, the mirror 3 and the mirror 4 may be moved to the right by the strict maintenance of speed ratio on the order of 2 : 1, thus attaining the desired end. Application of this optical system into a copying machine requires movement thereof in the form of a reciprocating motion. Thus, the supports 10 and 12 reached at the right extremity in the movable range shown in FIG. 1 are allowed to be returned to their original positions. For the returning means, there has been proposed one of which the elasticity of spring 13 is utilized as shown in FIG. 1, and the other of which a motor in place of the spring 13 is employed as drive means. However, in the method for returning the optical system by the elasticity of the spring, a spring greater in shape must be used where the optical system travels a long stroke, and as a result the spring would occupy a greater portion of space in the machine and hence the entire machine becomes larger in size. Additionally, acceleration due to the spring characteristic makes it hard to control a return speed and to further produce great shocks when the optical system is stopped at its initial position. The shocks cause the optical system to be vibrated, and better copied images may not be obtained before such vibration is damped. Obviously, the durability of the optical system, which is generally said to be not so slight in nature, is adversely affected by the spring.
Further, in the method for returning the optical system which uses the motor as drive means instead of springs, a sag is created in the wire due to the delay in start of the motor where the motor is rotated at high speeds to move the wire, and for this reason, the optical system may not be moved smoothly.
A method of wiring electric cords for illuminating an original will now be discussed. In a conventional copying machine wherein an original is placed on a stationary carriage, and optical mirrors including a light source are moved at a ratio of 1 : 1/2 for a copying process, there are two methods for arranging electric cords connected to the above-mentioned optical system. Firstly, in accordance with the first method, an electric cord having a length corresponding to that of the whole stroke of movement of the optical system is pre-attached to the moving optical system, and a portion of the cord sagged due to the movement of the optical system is left to be hung in a space. Secondly, in accordance with the second method, there are incorporated a rail-like member in conductive condition and an electricity receiving contact used in the moving optical system. These conventional methods suffer from the following problems. In the first method above, holding parts on the opposite ends of the electric cord are subjected to severe damage due to the stress caused by the sagging of the cord created because of movement of the optical system. Moreover, the sagged cord tends to come into contact or to be caught in other parts of the machine, thus not only interfering with a smooth operation but involving risk such as damage to insulation covering of the cord. As for the problems encountered in the second method above, it is not possible to coat the rail-like member, in which a great current flows, with an insulation covering in view of such object that current is passed while being slid thereon, and it is not preferable from a standpoint of safety that the rail without having the covering as described above is disposed within the machine. Furthermore, faulty contact tends to be created between the contact and the rail member, and the image formed becomes discontinuous due to the occurrence of sparks or interruption of current. Additionally, the severe wear of the contact results in a troublesome maintenance such as replacement of the contact and the like.